* Expand allowedUsers email field to support comma-separated and domains
Closes#8
* Refactor AuthFetch() to return AuthUser struct
Also, this breaks out a parseLine() function which can be easily tested.
* Ignore empty addrs after splitting commas
This ignores a trailing comma
* Add tests for auth parseLine()
* Update documentation in smtprelay.ini
* Fix bug where addrAllowed() was incorrectly case-sensitive
* Update allowedUsers allowed domain format to require leading @
This disambiguates a local user ('john.smith') from a domain ('example.com')